Shipwrecks have a decent chance of being well-preserved in the low-salt waters of the Stockholm archipelago because of the lack of wood-eating shipworms.

If the entire ship — the size and type of which are unclear — is still intact, its cargo could give historians a better idea of trading that took place in the area at the time.

There is a large crack in the hull, which had been covered by a piece of leather that had been nailed to the boards, Hjulhammar said.

"That is a sign that this ship was very worn down, and it is possible that this repair work is part of the reason it sank," he said. "My spontaneous reaction was that the repair was rather clumsily done."

The museum is awaiting permission from the county government to dig out the remaining parts of the ship, Hjulhammar said. They would then decide whether it is possible to bring it up on land.

"But it depends on how eroded it is," he said. "It may turn out that it is better to let her lie."